JPS62252005A - Ferrodielectric thin film device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a ferroelectric thin film element used in pyroelectric infrared detection elements, piezoelectric elements, electro-optical elements, and the like.

BACKGROUND ART There are various applications of ferroelectric materials in the electronics field, such as infrared detection elements, piezoelectric elements, light modulation elements, and memory elements. As electronic components become smaller due to advances in semiconductor technology in recent years, ferroelectric elements are also becoming thinner.

By the way, in pyroelectric infrared detection elements, piezoelectric elements, etc. that extract changes in the spontaneous polarization Ps of a ferroelectric material as an output, the largest output can be obtained when the Ps of the ferroelectric material is aligned in one direction. .

Problems to be Solved by the Invention Currently, the ferroelectric ceramics used in infrared detection elements, piezoelectric elements, etc. are polycrystalline, and there is no directionality in the arrangement of crystal axes, so if spontaneous polarization Ps occurs. Arranged in the eye.

In epitaxial ferroelectric thin films and oriented ferroelectric thin films, the crystal polarization axes are aligned, but the electrical spontaneous polarization Ps is 1.
80° domains are created and arranged alternately. Therefore,
When these materials are used as electronic devices as described above, a polarization process is required to apply a high electric field (~100 kV/cm) to the materials to align the directions of Ps.

In addition, there are many reports on the production of thin films such as PbTiO3 and PLZT, but for thin films in the ferroelectric phase region, thin films oriented along the C axis, which is the polarization axis, and even spontaneous polarization are oriented in one direction. A thin film with this effect has not yet been realized.

The following problems arise in the method of aligning Ps by applying a high electric field to a ferroelectric material.

(1) Dielectric breakdown may occur due to polarization treatment, resulting in lower yield.

(2) In a high-resolution array element in which a large number of microelements are arranged at high density, it is difficult to polarize them uniformly.

(3) In an integrated device in which a ferroelectric thin film is formed on a semiconductor device, polarization itself may not be possible in some cases.

Means to solve the problem As a ferroelectric thin film, the chemical formula is (PbxLay)(T
iz2rw) O+ and the composition ratio is (a) 0.70≦x≦L O, 9≦x+y≦L O,
95≦z≦11(b) x-1, y==0, 0.45≦
z<lSz+w-1, (c) 0.83≦x<1, x+
It is in one range selected from y-110,5≦z<1゜0.96≦z+-≦1, the film thickness is 4 μm or less, and 758 or more of its polarization axes are oriented in one direction. use something

Effect In the ferroelectric thin film as described above, natural polarization with Ps already aligned can be obtained, and there is no need for polarization treatment.
High yield (and high performance ferroelectric elements can be realized).

Embodiment FIG. 1 is a sectional view of an embodiment of a ferroelectric thin film element manufactured according to the present invention.

A substrate 1 was an MgO single crystal that had been mirror-polished with (100), and a Pt thin film having a thickness of 0.2 μm was formed as a lower electrode 2 by sputtering. The sputtering gas is Ar-
02 mixed gas. Then, the ferroelectric thin film 3 was coated with a thickness of 0.5
It was grown to ~8 μm. The method was high-frequency magnetron sputtering, using a mixed gas of Ar and 02, and the sputtering target was 1 (1-Y)PbxLayTizZr-Os +YP.
bO1'' (1) powder. Table 1 shows the sputtering conditions.

Next, a Ni--Cr electrode was deposited as an upper electrode 4 on this thin film to produce a ferroelectric thin film element. Furthermore, an opening 5 was provided in the substrate 1 below the ferroelectric thin film 1llI3.

Table 1 Figure 2 shows the X-ray diffraction pattern of a typical thin film. Only the (001) and (100) reflections of the perovskite structure and their higher-order reflections are observed. Furthermore, since the intensity of the (001) reflection is significantly larger than that of (100), it can be seen that it is a C-axis oriented film. The C-axis orientation rate α is defined by the following equation.

α(oo++/1l(oo+)+I(too)1 where I(0011 and 1(too) are respectively (00
1) and represents the diffraction intensity of (100) reflection. The dielectric constant and pyroelectric coefficient of the obtained thin film were measured.

Figure 3 shows the pyroelectric coefficient γ of PbTiOs with respect to the C-axis orientation rate.
Figure 4 shows the change in dielectric constant ε.

As is well known, the pyroelectric coefficient increases in proportion to the orientation of the spontaneous polarization Ps. The pyroelectric coefficient increases as the orientation rate increases, and the dielectric constant decreases. FIGS. 3 and 4 also show the results when polarization treatment (applying 100 kV/cwflO at 200° C.) was performed. When the orientation rate is small, the values of the pyroelectric coefficient and permittivity change significantly before and after the polarization treatment. When the orientation rate becomes 75 zero, the pyroelectric coefficient becomes 1.6xlO'C/cdK, and this value is 200°C.
PbTiO3 ceramics (y-1,8xlO-'C/
cjK). When the orientation rate is 80 zero, the pyroelectric coefficient is 2.5xlO-tic/cjK, and PbT
This value is considerably larger than that of iOs ceramics. Moreover, not only is it almost the same as the value after polarization treatment, but it is also larger than the value after polarization when the orientation rate is small. When the orientation rate is 75z, the dielectric constant is about 100, which is half the value of ceramics.
It is. The same results were obtained with PbTiC)3(PLT) doped with La.

As mentioned above, p b TiO3 and PLT thin films do not require polarization treatment if they are sufficiently oriented along the C axis during thin film production (but the spontaneous polarization is uniform, especially when the orientation rate is 7).
It has become clear that the effect is large when the thickness of the film is 5% or more.

By the way, it has been found that the C-axis orientation rate of a thin film changes depending on the film thickness. FIG. 5 shows the relationship between the C-axis orientation rate and the film thickness. As is clear from the figure, the C-axis orientation rate decreases significantly as the film thickness increases. C if the film thickness exceeds 8 μm
The degree of orientation of the axis drops to about 60% on average. Therefore, natural polarization with Ps already aligned can be obtained by
It is desirable that the film thickness be approximately 4 μm or less.

Exactly the same results were obtained when Au was used as the lower electrode.

When the ferroelectric thin film element produced in this example is used as an infrared sensor, the figure of merit as a pyroelectric material is [
The value of pyroelectric coefficient/permittivity 1 increases. 10 at 200℃
Compared with the value of PbTiO3 ceramics subjected to polarization treatment by applying 100 kV/c+s for minutes, PbTi
2.5 times more with O3 thin film, PLTfil! 3 times the value.

In other words, it can be seen that by using the ferroelectric thin film according to the present invention, an infrared sensor with excellent characteristics can be produced without any polarization treatment.

As can be seen from the above example, the device using the ferroelectric thin film of the present invention can produce a large output even without polarization processing. The same is true.

Effects of the Invention The ferroelectric thin film element according to the present invention does not require polarization treatment, has excellent characteristics, and is easy to manufacture, so it is extremely effective in practice.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a ferroelectric thin film element in an embodiment of the invention, FIG. 2 is a diagram showing an X-ray diffraction pattern of a ferroelectric thin film in an embodiment of the invention, and FIG. 3 is a C FIG. 4 is a diagram showing the relationship between the axial orientation rate and the pyroelectric coefficient, FIG. 4 is a diagram showing the relationship between the C-axis orientation rate and the dielectric constant, and FIG. 5 is a diagram showing the relationship between the C-axis orientation rate and the film thickness. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Lower electrode, 3... Ferroelectric thin film, 4... Upper electrode, 5... Opening. Name of agent Patent attorney Toshio Nakao and 1 other person Figure 1 Figure 2 Figure 3 θ6 =0, f3 1. Ocm orientation Hizawa Fig. 4 0 Hiramushi Nishiki σ bow rate: Bi, Fig. 5 0.5 / 2 4
8 pancreatic thickness (, a desk)

Claims (4)

[Claims] (1) A substrate, formed on the substrate, and having the chemical formula (Pb
_xLa_y)(Ti_zZr_w)O_2 and the composition ratio is (a) 0.70≦x≦1, 0.9≦x+y≦1, 0.9
5≦z≦1, w=0, (b) x-1, y-0, 0.45≦z<1, z+w=1
, (c) 0.83≦x<1, x+y=1, 0.5≦z<1
, 0.96≦z+w≦1, and the film thickness is 4 μm.
What is claimed is: 1. A ferroelectric thin film element comprising a ferroelectric thin film having a ferroelectric thickness of about 100% or less, and an electrode attached to the ferroelectric thin film, wherein 75% or more of the polarization axes of the ferroelectric thin film are oriented in one direction. (2) One or more lower electrodes formed on the substrate, a ferroelectric thin film formed on the lower electrode, and one electrode provided on the ferroelectric thin film facing the lower electrode. A ferroelectric thin film element according to claim 1, comprising the above upper electrode. (3) A ferroelectric thin film element according to claim 1, wherein the substrate is MgO. (4) The ferroelectric thin film element according to claim 1, wherein the lower electrode is made of Pt or Au.